According to the prior art, automatic transmissions, especially for motor vehicles, comprise planetary gearsets that are shifted by means of friction elements or shifting elements, such as clutches and brakes, and are usually connected to a starting element that is subjected to a slip effect and is selectively provided with a lockup clutch, such as a hydrodynamic torque converter or a fluid clutch.
Within the scope of DE 101 15 983 A1 of the applicant, for example, a multi-speed transmission is described comprising an input shaft, which is connected to a front-mounted gear set, an output shaft, which is connected to a rear-mounted gear set, and a maximum of seven shifting elements, whose selective shifting allows at least seven forward gears to be shifted into without a range shift. The front-mounted gear set consists of one shiftable or non-shiftable planetary gearset or a maximum of two non-shiftable, mutually coupled planetary gearsets. The rear-mounted gear set is configured as a two-carrier, four-shaft transmission with two shiftable planetary gearsets, and has four free shafts. The first free shaft of this two-carrier, four-shaft transmission is connected to the first shifting element, the second free shaft is connected to the second and third shifting elements, the third free shaft is connected to the fourth and fifth shifting elements, and the fourth free shaft is connected to the output shaft. For a multi-speed transmission with a total of six shifting elements, it is proposed according to this prior invention to additionally connect the third free shaft or the first free shaft of the rear-mounted gear set to a sixth shifting element. For a multi-speed transmission with a total of seven shifting elements, it is proposed according to this prior invention to additionally connect the third free shaft to a sixth shifting element, and to additionally connect the first free shaft to a seventh shifting element.
Several other multi-speed transmissions are known, for example, from German Patent 101 15 995 A1 of the applicant, in which four shiftable, mutually coupled planetary gearsets and six or seven frictionally engaging shifting elements are provided, whose selective engagement allows a rotational speed of an input shaft of the transmission to be transmitted to an output shaft of the transmission in such a way that nine or eleven forward gears and at least one reverse gear can be shifted into. Two or three shifting elements are engaged in each gear according to the schematic diagram, while during a change from one gear to the respectively following higher or lower gear, only one engaged shifting element is disengaged in order to prevent range shifting, and a previously disengaged shifting element is engaged.
In the related unpublished patent application DE 102005002337.1 of the applicant, a multi-speed transmission is furthermore proposed with an input shaft, an output shaft, four mutually coupled separate planetary gearsets, and five shifting elements, in which eight forward gears can be shifted into without range shifting, that is, in such a way that during a change from one forward gear into the following higher or lower forward gear, respectively only one of the previously engaged shifting elements is disengaged and only one of the previously disengaged gears is engaged. The multi-speed transmission also has a reverse gear. Three shifting elements are respectively engaged in all forward gears and in the reverse gear. With respect to the kinematic coupling of the four planetary gearsets among each other and to the input shaft and output shaft, it is provided that a carrier of the fourth planetary gearset and the input shaft are connected to each other and form a first shaft of the transmission, a carrier of the third planetary gearset and the output shaft are connected to each other and form a second shaft of the transmission, a sun gear of the first planetary gearset and a sun gear of the fourth planetary gearset are connected to each other and form a third shaft of the transmission, a ring gear of the planetary gearset forms a fourth shaft of the transmission, a ring gear of the second planetary gearset and a sun gear of the third planetary gearset are connected to each other and form a fifth shaft of the transmission, a carrier of the first planetary gearset and a ring gear of the third planetary gearset are connected to each other and form a sixth shaft of the transmission, a sun gear of the second planetary gearset and a ring gear of the fourth planetary gearset are connected to each other and form a seventh shaft of the transmission, and a carrier of the second planetary gearset forms an eighth shaft of the transmission. With regard to the kinematic coupling of the five shifting elements to the four planetary gearsets and to the input shaft and output shaft, it is provided that the first shifting element is arranged in the direction of power flow between the third shaft and a housing of the transmission, the second shifting element is arranged between the fourth shaft and the housing of the transmission, the third shifting element is arranged between the first and fifth shafts, the fourth shifting element is arranged either between the eighth and second shafts or between the eighth and the sixth shafts, and the fifth shifting element is arranged either between the seventh and fifth shafts or between the seventh and eighth shafts or between the fifth and eighth shafts.
Automatically shiftable motor vehicle transmissions of planetary construction have already been frequently described in the prior art and are being continuously developed and improved. These transmissions should have a sufficient number of forward gears as well as one reverse gear with a transmission ratio having a high overall spread as well as very advantageous progressive ratios, which are well suited for motor vehicles. They should further enable a high startup transmission ratio in the forward direction, and should include a direct gear and should be suitable for use in passenger cars as well as in commercial vehicles. Furthermore, these transmissions should require a low construction expenditure, in particular a small number of shifting elements, and should prevent double shifting in sequential shifting mode, so that only one shifting element is changed during shifting into the defined gear groups.